In most modern office buildings, a room's ceiling does not attach to the uppermost surface of the room. Rather, a suspension system supports the ceiling at a distance below the upper surface. A plenum then represents the space between the room's uppermost surface and its ceiling.
Classically, a suspended ceiling has taken one of two different forms. The first employs runners of an appreciable width which remain visible at all times. Intersecting pairs of parallel runners serve to define a rectangular open space between them. A ceiling tile of an appropriate dimension sits on top of the runners where it stays under the influence of gravity. The outer perimeter of the tile has a greater dimension than the defined space between the runners. To remove a tile simply involves lifting the tile off the runners and manipulating it through its own opening. Alternately, a tile can move to an adjacent space and rest temporarily upon another tile. Installing a tile merely requires placing it through the opening and resting it with the flat, pleasing appearance facing downwards and its edges resting on the runners.
The type of gravity-held ceiling system described above has various natural advantages. Any tile may undergo removal to permit access to the plenum at its location. Substitution of a new tile, concommitantly, represents a very facile task.
However, the runners do not always present a pleasing appearance. They necessarily constitute strips of substantial width which always remain accessible to view. Thus, the ceiling has a grid pattern of these strips marring the appearance presented by the tiles themselves. Furthermore, the junctures where the runners cross may prove even less aesthetically pleasing.
Additionally, the tiles do not have positive placement on the runners. As a consequence, slight movement may cause an edge of a tile to become visible.
An alternative system finding frequent use does not employ visible runners. This system employs kerfed and back-cut tiles. The support system for this type of ceiling employs hidden runners that interconnect the tiles together. The visible bottoms of the tiles contact each other to provide a desirable appearance.
However, removing the tiles represents a difficult task at best. Only a small number of the tiles may undergo removal without first affecting the other tiles. To obtain access to the plenum above the tiles or replacing a damaged tile at a specific location may require the removal of a substantial portion of the ceiling. Furthermore, the person seeking access to the plenum or removing a tile must know which individual tiles in particular must undergo initial removal.
Various modifications to the two systems described above have attempted to ameliorate at least some of their drawbacks. A. A. Mancini, in his U.S. Pat. No. 3,087,205, and P. D. Dail, in his U.S. Pat. No. 2,994,113, use kerfed tiles adjoined into rows through interconnecting splines. However, on the free edges, they attach a bracket with hooks. These hooks sit on an upstanding edge of a runner suspended from the upper surface. The tiles thus all have a positive connection to other tiles and rest on the suspension system. Moreover, removing an entire row represents a relatively facile task.
However, Mancini and Dail have a number of drawbacks from the two basic types of systems described above. They still has relatively wide runners that detract from the appearance of the ceiling. Moreover, their systems do not permit the facile removal of individual tiles; an entire row going across the room must undergo removal at the same time. At the very minimum, removing one tile affects its neighbors.
U.S. Pat. No. 4,089,146 to V. Martinez, shows a system which similarly includes rows of tiles linked to each other with cross T's inserted in their kerfed sides. One end of each tile also has kerfing. This slot receives, in a close friction fit, a flange of a main supporting runner. A hook forming part of the cross T attaches to a second runner to hold the other end of the tile in place. A special tool permits the disengagement of the hook from the runner to initiate removal of a tile.
Again, Martinez has rows of tiles attached to each other. He does not provide a facile method for removing a single tile at a time. Furthermore, removal of any of the tiles requires the tool and a knowledge as to where to use the instrument. Again, access to a particular area of the plenum or the removal of a particular tile in general represents a complicated task.
K. Oide, in his U.S. Pat. No. 4,057,947, provides a ceiling system which does not require exposed runners. Oide provides T-shaped clips inserted into the tiles' kerfing. The extended leg may then fold over joists attached to the room's upper surface to attach the tiles. Oide, however, does not address himself to the problem of the facile removal of individual tiles.
W. M. Erikson, in his U.S. Pat. No. 2,993,240, provides a ceiling with contacting tiles. Cross T's inserted in the tiles' kerfings holds them together. However, a number of the tiles have a sufficient backcutting that in fact the kerfing disappears, leaving only a lower ridge. Without an upper flange, the cross T's do not support these tiles. To keep these tiles in place, they have moveable slides which can rest on runners to support the ends of these tiles. Tongues depending through spaces between tiles allow repositioning of the slide for the insertion and removal of the tiles. However, the tongues themselves detract from the smooth surface of the ceiling. Moreover, only a limited number of the tiles have this removable feature. Accordingly, the removal of any particular tile or access to the plenum at that particular location may require the disassembly of other portions of the ceiling.
In M. D. Jahn's U.S. Pat. No. 3,832,816, parallel runners with upturned edges support the ends of tiles linked together in rows. The lower surface of the tiles has kerfing into which fit the upturned edges of the runners. By moving a portion of material on the lower surfaces at the edges of the tiles permits the runners to have a recessed location between tiles. However, the runners still remain visible. Furthermore, they must have sufficient width to support the edges of two adjacent rows of tiles. Moreover, adjacent tiles in a row may only touch each other with no connection or, alternatively, with a tongue and groove or lap joint. In the former case, the edges of the tile do not receive support from each other. In the latter, removal of an individual tile again proves problematic.
L. G. Stahlhut's U.S. Pat. No. 3,287,874 has a grid pattern of runners. A bevel on the edge of the runners holds flanges or extending lugs cut from the edges of the tiles. Flexing the tiles permits their insertion and removal. However, the runners must have sufficient width to allow for the entrance of clips used to hold the runners to the room's upper surface. Furthermore, a space must separate the bottoms of the tiles from the runners; the space allows the flexing of the tiles for their insertion or removal. Furthermore, the system requires a tile having sufficient structural integrity for their lugs to rest on the extending bevels and not crumble under their own weight.
Accordingly, the search continues for a ceiling system which permits the facile removal of any individual tile. Yet, to achieve a pleasing aesthetic appearance, the runners used should not seriously detract from the ceiling's appearance.